Expandable vertebral implant

ABSTRACT

The present invention relates to an expandable implant for engagement between vertebrae generally comprising an inner member, outer member, and gear member positioned coaxial with respect to each other such that the inner and outer members are moveable relative to each other along an axis. The gear member is axially fixed to the outer member and freely rotatable with respect to the outer member and the gear member threadedly engages a threaded portion of the inner member to translate inner member along the axis. The implant is configured to engage the vertebrae in a predetermined alignment and the gear member includes gear teeth exposed to the exterior and configured to be accessible by a tool member at a plurality of angular positions around the perimeter of the implant device.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 13/606,625, filed Sep. 7, 2012, which is a continuation of U.S.patent application Ser. No. 12/758,529, filed Apr. 12, 2010, now U.S.Pat. No. 8,282,683, the entire disclosures of which are incorporatedherein by reference in their entireties for all purposes.

FIELD OF THE INVENTION

The present invention relates to a device to support the spine afterremoval of at least a part of a vertebra.

BACKGROUND OF THE INVENTION

When a vertebra is damaged or diseased, surgery may be used to replacethe vertebra or a portion thereof with a prosthetic device to restorespinal column support. For example, vertebral body replacement iscommonly required in the treatment of vertebral fracture, tumor, orinfection.

In recent years, several artificial materials and implants have beendeveloped to replace the vertebral body, such as, for example, titaniumcages, ceramic, ceramic/glass, plastic or PEEK, and carbon fiberspacers. Recently, various expandable prosthetics or expandable cageshave been developed and used for vertebral body replacement. Theexpandable prosthetic devices are generally adjustable to the size ofthe cavity created by a corpectomy procedure and typically are at leastpartially hollow to accommodate bone cement or bone fragments tofacilitate fusion in vivo. Some expandable implants may be adjustedprior to insertion into the cavity, while others may be adjusted insitu. Two advantages of the vertebral body replacement using anexpandable prosthetic device that is adjustable in situ is that it iseasy to place or insert and it permits an optimal, tight fit andcorrection of the deformity by in vivo expansion of the device. Someother advantages offered by an expandable prosthetic device are thatthey can facilitate distraction across the resected vertebral defect forcorrection of the deformity, and allow immediate load bearing aftercorpectomy.

Instrumentation and specialized tools for insertion of a vertebralimplant is one important design parameter to consider when designing avertebral implant. Spinal surgery procedures can present severalchallenges because of the small clearances around the prosthetic when itis being inserted into position. Another important design considerationincludes the ability of the device to accommodate various surgicalapproaches for insertion of the vertebral implant.

SUMMARY OF THE INVENTION

The present invention relates to an expandable prosthetic implant devicefor engagement between vertebrae generally comprising an inner member,outer member, and gear member positioned coaxial with respect to eachother such that the inner and outer members are moveable relative toeach other along an axis. The inner member has a hollow interior portionand a threaded external portion and includes a first end portionconfigured to engage an endplate which is capable of engaging a firstvertebral body. The outer member has a hollow interior portionconfigured to receive the inner member and includes a second end portionconfigured to engage an endplate which is capable of engaging a secondvertebral body. The gear member is axially fixed to the outer member andfreely rotatable with respect to the outer member and the gear memberthreadedly engages the threaded portion of the inner member.

The implant is configured to engage the vertebrae such that first andsecond end portions are oriented in a predetermined alignment withrespect to the first and second vertebral bodies. The gear memberincludes teeth extending around the perimeter of the gear member and theteeth are exposed to the exterior and configured to be accessible by atool member.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be more readily understood with reference tothe embodiments thereof illustrated in the attached drawing figures, inwhich:

FIG. 1 is a perspective view of an implant in accordance with anembodiment of the present invention;

FIG. 2 is an exploded view of the implant of FIG. 1;

FIG. 3 is a cross-sectional view of the implant of FIG. 1 taken alongline 3-3 of FIG. 1;

FIG. 4 is perspective view of an embodiment of an inner member of theimplant of FIG. 1;

FIG. 5 is perspective view of an embodiment of an outer member of theimplant of FIG. 1;

FIG. 6 is an elevated perspective view of one embodiment of a gearmember of the implant of FIG. 1;

FIG. 7 is a bottom perspective view of the gear member of FIG. 6;

FIG. 8 is a perspective of one embodiment of a tool according to thepresent invention;

FIG. 9 is a cross-sectional view of the tool of FIG. 8 shown engaging anembodiment of an expandable implant according to the present invention;

FIG. 10 is a perspective view of another embodiment of an implantaccording to the present invention; and

FIG. 11 is a perspective view of another embodiment of an endplate of animplant according to the present invention;

FIG. 12 is an exploded view of the endplate of FIG. 11; and

FIG. 13 is a cross-sectional view of the endplate of FIG. 11.

Throughout the drawing figures, it should be understood that likenumerals refer to like features and structures.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiments of the invention will now be described withreference to the attached drawing figures. The following detaileddescription of the invention is not intended to be illustrative of allembodiments. In describing preferred embodiments of the presentinvention, specific terminology is employed for the sake of clarity.However, the invention is not intended to be limited to the specificterminology so selected. It is to be understood that each specificelement includes all technical equivalents that operate in a similarmanner to accomplish a similar purpose.

Referring to FIGS. 1-6, a preferred embodiment of an expandablevertebral implant 10 is shown. The implant 10 preferably comprises aninner member 12 which may be telescopingly received within an outermember 14. The implant 10 further comprises a gear member 16 generallyconfigured to effect translation of the inner member 12 with respect tothe outer member 14 thereby allowing for expansion and contraction ofthe implant 10. The inner member 12, the outer member 14, and the gearmember 16 are preferably centered along a longitudinal axis 18 anddefine a hollow interior portion which may be filled with bone material,bone growth factors, bone morphogenic proteins, or other materials forencouraging bone growth, blood vessel growth or growth of other tissuethrough the many apertures in the device. In one preferred embodiment,members 12, 14, and 16 are made of a polyether ether ketone (PEEK)plastic material. There are several known advantages of PEEK plasticmaterial including being radiolucent, having a mechanical strength thatis close to bone, and may be more easily sterilized than other plastics.In alternate preferred embodiments, the members 12, 14, and 16 may bemade of a biologically inert metal alloys, such as titanium, or othersuitable materials.

Referring to FIGS. 1-5, the inner member 12 has a generally cylindricalbody 24 with a distal end 22 and a proximal end 36. In a preferredembodiment, the body 24 of the inner member 12 comprises an innersurface 28 and an outer surface 30 and generally defines a hollowinterior portion 23 extending axially therethrough. At least part of theouter surface 30 preferably includes external threads 32. Locatedproximate to the distal end 22 of the body 24 are a plurality of tabs 38which assist in connecting and positionally locating an endplate 20. Ina preferred embodiment, the body 24 is configured and dimensioned to becooperatively received within outer member 14.

The outer member 14 has a generally cylindrical body 40 with a distalend 42 and a proximal end 44. In a preferred embodiment, the body 40 ofthe outer member 14 comprises an inner surface 46 and an outer surface48 and generally defines a hollow interior portion 50 extending axiallytherethrough. The outer surface 48 preferably has at least one slot 52and an opening 54 configured and dimensioned to receive a portion of animplantation tool. In a preferred embodiment, the opening 54 extendsfrom the outer surface 48 to the hollow interior portion 50 and at leasta portion of the opening 54 is threaded. As best seen in FIG. 5, theinner surface 46 includes a channel 57 for receiving a locking member(discussed below). Located proximate to the proximal end 44 of the outermember 14 are a plurality of tabs 60 which assist in connecting andpositionally locating an endplate 62. In a preferred embodiment, a lip362 is formed around the exterior of the distal end 42 of body 40 and isconfigured to cooperatively fit with a portion of the gear member 16. Aplurality of relief spaces or slots 64 are radially spaced around lip362 to facilitate a snapping engagement of the lip 362 with the gearmember 16. In this regard, slots 64 allow the lip 362 to deform slightlyand contract in the radial direction to accommodate gear member 16 tosnap on to lip 362. In a preferred embodiment, the interior portion 50of body 44 is configured and dimensioned to cooperatively receive body24 of inner member 12 within outer member 14. In this regard, thedimensions of interior portion 50 of body 44 are greater than dimensionsof body 24 of inner member 12.

As best seen in FIGS. 2-5, in a preferred embodiment of a prostheticdevice 10, the body 24 of the inner member 12 includes a flattenedportion 34 which extends at least in part from the distal end 22 to theproximal end 36 and includes a base member 37 having at least one lobe39 located proximate to the distal end 36 of the body 24. Focusing onFIG. 5, the body 40 of the outer member 14 includes a flattened area 56and at least one depression 58 on the inner surface 46. When the innermember 12 is assembled within the outer member 14, the flattened area 56of the outer member 14 cooperatively aligns with the flattened portion34 of the inner member 12 and the at least one depression 58 of outermember 14 receives the at least one lobe 39 of the inner member 12. Theflattened portion 34 and the flattened area 56 along with the lobes 39and the depressions 58 cooperate to allow the inner member 12 tolinearly move with respect to the outer member 14 but prevent the innermember 12 from rotating with respect to the outer member 14. Inaddition, the base member 37 serves as a stop preventing the innermember 12 from rotating to a point of disengagement from outer member14.

Referring now to FIGS. 6-7, a gear member 16 comprises a generallyhollow body 364 extending from a distal end 66 to a proximal end 68 witha helical thread 70 along at least part of an inner wall 72 and an arrayof gear teeth 74 along a portion of the exterior wall 75. The gearmember 16 is generally configured to rotatably connect to the distal end42 of the outer member 14 and the internal helical thread 70 isconfigured to engage the external threads 32 of the inner member 12 tocause translation of the inner member 12 with respect to the outermember 14. In a preferred embodiment, the gear member 16 includes acylindrical cutout feature 76 extending around the inner wall tocooperatively receive the lip 54 of the outer member 14. In this regard,the gear member 16 may rotate freely with respect to the outer member 14while being retained from longitudinal and lateral movement. In apreferred embodiment, the gear member 16 also includes a series ofcutouts 73 located proximate to the proximal end 68 for engaging aportion of a locking member.

With continued reference to FIGS. 6-7, the gear teeth 74 extendsubstantially from the proximal end 68 to the distal end 66 and extendaround the entire periphery of at least a portion of the exterior wall75. The outer-most external diameter 78 of the gear member 16 is sizedto be the same as or slightly smaller than the smallest outer diameterof the endplates 20, 62 and the outer member 14. In this regard, whenthe implant 10 is viewed from the end in a plane perpendicular to thelongitudinal axis 18, the gear member 16 does not protrude radiallyoutward from beyond the perimeter of the endplates 20, 62.

As shown in FIG. 7, in a preferred embodiment, the gear teeth 74 extenda width 380 in a generally radial direction and generally extendradially outward to the outer diameter of the gear member 16. In thisregard, the teeth 74 may be designed to have a width 380 to accommodatethe expected gear forces given the particular gear ratio, types ofmaterial used, and desired overall diameter of prosthetic device 10. Oneskilled in the art will appreciate that the larger the outer diameter towhich the teeth 74 radially extend, the larger the teeth 74 may bedesigned while still maintaining the same gear ratio. In this regard,when the teeth 74 are made larger, they generally have a bettermechanical strength. Also, the ability to design larger, wider, andstronger teeth 74 is advantageous for embodiments where the implant 10is made of PEEK, other plastic, or other non-metallic materials that mayhave less mechanical strength than, for instance, titanium.

Furthermore, as described in one embodiment, because the outer-mostdiameter of the gear member 16 may be as large as the outer diameter ofthe endplates 20, 62, and the teeth 74 extend radially to the outer-mostdiameter of the gear member 16, a larger inner diameter of the gearmember 16 may be manufactured without compromising mechanical gearstrength. As a result, a larger overall inner diameter of the implant 10may be accommodated which allows the packing of more bone materialtherein and facilitates bone fusion once the implant 10 is implanted.

As seen in FIGS. 1-3, in a preferred embodiment, the teeth 74 areexposed to the exterior of prosthetic device 10. Because the teeth 74are exposed around the periphery, little to no material is needed tocover up the exposed teeth, which generally makes the implant 10 lighterand easier to manufacture than prior art devices that require coveringthe gear teeth. In addition, the gear member 16 is more easily visibleby a surgeon and more readily accessible by a rotation tool than devicesthat hide or cover gear teeth.

Referring to FIGS. 2, 5, and 7, in a preferred embodiment, the implant10 also includes a locking member 80. The locking member 80 may beprovided to substantially restrict all relative movement between innermember 12 and outer member 14, when, for example, the desired expansionof the prosthetic device 10 has been obtained. The locking member 80 hasa body portion 82 with a through-hole 84. In a preferred embodiment, thebody portion 82 has at least one, but preferably two, outwardlyextending, flexible arms 86, 88 and at least one engagement member 90.In other preferred embodiments, instead of flexible arms 86, 88, it iscontemplated that the locking member 80 may include an alternate biasingmember, such as a leaf spring. The locking member 80 is configured anddimensioned to be received in the channel 57 of the outer member 14 insuch a manner that the arms 86, 88 rest against a shelf portion in thechannel 57 and the through-hole 84 partially aligns with opening 54. Theengagement member 90 preferably protrudes upwardly and is configured anddimensioned to engage the cutouts 73 of the gear member 16 to preventthe gear member 16 from rotating.

Referring now to FIGS. 1-3, in a preferred embodiment, the endplates 20,62 are shown wherein the endplate 20 connects to the inner member 12 andendplate 62 connects to the outer member 14. In a preferred embodiment,endplate 20 includes an extension portion 91 which is received in theinterior portion 23 of inner member 12, for example, in an interferenceor snap fit and includes a plurality of tabs 93 which interdigitate withtabs 38 to connect and position endplate 20 with respect to the innermember 12. Endplate 62 includes an extension portion 95 which engagesthe proximal end 44 of the outer member 14, for example, in aninterference or snap fit and includes a plurality of tabs 97 whichinterdigitate with tabs 60 to connect and position endplate 62 withrespect to the outer member 14. The endplates 20, 62 also preferablyinclude hollow interior portions 99, 101 which are in fluidcommunication with the hollow interior portions 23, 50 of inner member12 and outer member 14, respectively.

In a preferred embodiment, each endplate 20, 62 is generally annular inshape when viewed from the end or perpendicular to the longitudinal axis18. It is, however, contemplated that the endplates 20, 62 can be othershapes including oblong, elliptical, kidney bean, polygonal, orgeometric. Preferably, the endplates 20, 62 are designed to resemble ormimic the footprint of the vertebral body to which the endplates willengage. In this regard, endplates 20, 62 are configured to engageportions of the vertebrae in a predetermined orientation to maximizecontact of the superior surface of the endplates 20, 62 with bone.

The dimensions of endplates 20, 62 can be varied to accommodate apatient's anatomy. In some embodiments, the endplates 20, 62 have awedge-shaped profile to accommodate the natural curvature of the spine.In anatomical terms, the natural curvature of the lumbar spine isreferred to as lordosis. When implant 10 is to be used in the lumbarregion, the angle formed by the wedge should be approximately between3.5 degrees and 16 degrees so that the wedge shape is a lordotic shapewhich mimics the anatomy of the lumbar spine. In alternate embodiments,the wedge shape profile may result from a gradual increase in heightfrom an anterior side to a posterior side to mimic the naturalcurvature, kyphosis, in other regions of the spine. Thus, in otherembodiments, the angle may be between about −4 degrees and −16 degrees.

As shown in FIGS. 1-3, in a preferred embodiment, the endplates 20, 40include a plurality of mounting holes 92 spaced around the perimeter ofeach endplate 20, 40 for receiving insertable bone engaging members 94.In one embodiment, bone engaging members 94, comprise conical spikes 96each having a cylindrical base portion 98 configured to fit within holes92, for instance, by press-fit or by threaded engagement. In alternateembodiments, differently shaped bone engaging members 100 may be used,or in other embodiments no bone engaging members may be used. Referringagain to FIG. 2, according to one embodiment, endplates 20, 62 havechamfered edges 100 around the perimeter to facilitate insertion and/oraccommodate the shape of the vertebral bodies which they engage. Thesuperior or bone engaging surfaces 102, 104 of endplates 20, 62 may alsoinclude numerous types of texturing to provide better initial stabilityand/or grasping contact between the end plate and the respectivevertebrae. In a preferred embodiment, the texturing is a plurality ofteeth 106. In preferred embodiments where the implant 10 is manufacturedfrom PEEK or other plastic materials, the endplates 20, 62 may alsoinclude radio-opaque material, such as tantalum markers 108, which aidin providing location markers in radiographic images.

In preferred embodiments, the length, diameter, and shape of prostheticdevice 10 may vary to accommodate different applications, differentprocedures, implantation into different regions of the spine, or size ofvertebral body or bodies being replaced or repaired. For example,implant 10 may be expandable to a longer distance to replace multiplevertebral bodies. Also endplates 20, 62 can be sized and shaped as wellas positioned to accommodate different procedures and approached to thespine. For example, endplates 20, 62 may be made smaller for smallerstatured patients or for smaller regions of the cervical spine. Inaddition, it is not required that endplates 20, 62 be shaped and sizedidentically and in alternate embodiments they can be shaped or sizeddifferently than each other and/or include different bone engagingmembers or texturing.

Turning now to FIGS. 8-9, the implant 10 may be expanded by a tool 110that includes a gear member 112 at its distal end 114. The tool 110extends along a tool axis 114 and in operation the tool 110 isconfigured to engage the implant 10 such that the tool axis 114 isgenerally perpendicular to the longitudinal axis 18. The gear member 112is configured to engage teeth 74 of the gear member 16 such that whenthe gear member 112 is rotated about the axis of the tool 110, the gearmember 16 of the implant 10 is rotated about the longitudinal axis 18and the inner member 12 translates along the longitudinal axis 18 toeither expand or contract the implant 10. In a preferred embodiment, thetool 110 may include a central shaft 116 having a threaded distal tipportion 118 that extends distally beyond gear member 112 to facilitatelocation and mounting of tool 110 with the implant 10. The threadeddistal tip portion 118 preferably includes a generally conical endportion and may be configured to extend radially through the opening 54and threadably engage opening 54 in the outer member 14.

With continued reference to FIGS. 8-9, in one embodiment of prostheticdevice 10 at least one, but preferably a plurality of mounting featuresor slots 52 are provided along the outer surface 48 of outer member 14.The tool 110 includes at least one, but preferably two, articulatingarms 120, 122 that engage slots 52 for better engagement of the tool 110with the implant 10 during insertion of the implant 10. In anotherpreferred embodiment, the tool 110 may include arms 120, 122 that do notarticulate.

In an exemplary use of the tool 110 with the implant 10, the tool 110initially engages the slots 52 of the implant 10 via the arms 120, 122and gear member 112 engages gear member 16 via their respectiveinterdigitating teeth. A control member on the proximal end of the tool110 (not shown) is manipulated to advance the central shaft 116 towardopening 54. The threaded tip portion 118 enters into opening 54 engagingthe threads in opening 54 as well as engaging the through-hole 84 oflocking member 80. It is also contemplated that the central shaft 116 isnot movable with respect to the tool 110. In that embodiment, the entiretool 110 is moved so that the central shaft can enter and engage theopening 54 and the through-hole 84. As discussed earlier, thethough-hole 84 is offset from opening 54, thus, when threaded tip 118engages and advances into the opening 54 and the through-hole 84, thelocking member 80 is pulled downwardly, riding along the conical edge ofthe tip 118 until the through-hole 84 is aligned with the opening 54. Asthe locking member 80 is pulled downwardly, the arms 82, 84 are flexedand the engagement member 90 disengages from the cutout 73 of the gearmember 16 allowing the gear member 16 to rotate freely. The gear member112 of tool 110 is then rotated via opening 114 which, in turn, rotatesgear member 16. As discussed above, the rotation of gear member 16results in the movement of inner member 12 causing the implant 10 toeither expand or contract, depending on the direction the gear member 16is rotated. Once the desired height for implant 10 is achieved, the toolmember 110 is disengaged from implant 10. When the tool 110 is removed,the locking member 80 returns to the back to its initial positionbecause of the arms 82, 84 returning back to their unflexed, at-reststate. The initial position of locking member 80 prevents the gearmember 16 from turning because of the engagement of engagement member 90with the cutouts 73. In that regard, implant 10 is locked from movementwhen the locking member 80 is in its initial position.

The benefit provided by the present locking mechanism is that it allowsfor a positive lock that engages and disengages automatically with theengagement and disengagement of the tool 110 with the implant 10, whichminimizes the steps the surgeon must perform during the procedure.

Referring now to FIGS. 10-13, alternate preferred embodiments ofendplates for the expandable implant 10 are shown. Looking at FIG. 10,in one variation, the endplates 202 and outer member 204 each include atleast one screw hole 206, 208, but, preferably, each include two screwholes. The screw holes 206, 208 are configured and dimensioned toreceive screws 210, 212. In a preferred embodiment, the screw holes 206,208 are angled such that when the screws 210, 212 are seated in thescrew holes 206, 208, the screws 210, 212 will extend outwardly from thesuperior surface 214 of endplate 202 and inferior surface 216 of outermember 204. Endplate 202 and outer member 204 also preferably include alocking element 218, 220 which, in a first position, allow the screws210, 212 to back out from the seated position and, in a second position,block the screws 210, 212 from backing out of the seated position. In anexemplary use, once the implant 200 is installed and expanded to thedesired position, the screws 210, 212 can be installed through the screwholes 206, 208 in such a manner as to purchase into the adjacentvertebral bodies. Once the screws 210, 212 are properly installed,including being engaged with the adjacent vertebral bodies, the lockingelements 218, 220 can be actuated to block the screws 210, 212 frombacking out of their installed position. The inclusion of screws 210,212 in the endplate 202 and the outer member 204 provides for additionalfixation of the implant 200 in the intervertebral space.

Turning to FIGS. 11-13, another preferred embodiment of an endplate 250is shown. The endplate 250 is similar to endplate 20 but includes theadditional functionality of being poly-axially rotatable with respect toan implant. In a preferred embodiment, endplate 250 includes a generallyarcuate extension portion 252 which is received in an interior portion253 of a receiving member 254 in such a manner as to allow the endplate250 to move poly-axially with respect to the receiving member 254.

In a preferred embodiment, the receiving member 254 is received in aninterior portion 255 of a locking ring 256. The receiving member 254preferably includes a neck portion 258 as well as a plurality of tabs260. The neck portion 258 is configured and dimensioned to be receivedwithin a hollow interior of an inner member, for example, in aninterference or snap fit, and the plurality of tabs 260 interdigitatewith tabs to connect and position the receiving member 254 with respectto an inner member. The receiving member 254 further includes aplurality of fingers 262 configured to cooperatively receive theextension portion 252 of endplate 250. A plurality of relief spaces orslots 264 are radially spaced between fingers 262 to allow fingers 262to bend or flex radially.

In a preferred embodiment, the locking ring 256 has a generally annular,c-shape and includes an exterior wall 266, an interior wall 268, andends 277, 279. The interior wall 268 preferably defines and interiorportion 255. In a preferred embodiment, the interior wall 268 includes aplurality of channel 270 which are spaced radially along the lockingring 256. The channels 270 allow the locking ring 256 to bend or flexradially. The ends 277, 279 each include openings 280, 282 which may bepartially threaded. A locking element 284 is configured and dimensionedto be threadingly received in the openings 280, 282. It alsocontemplated that that locking element 284 can engage the ends 277, 279by other non-threaded means, such as a sliding fit.

With continued reference to FIGS. 11-13, in a preferred embodiment, theendplate 250 includes a plurality of mounting holes 286 spaced aroundthe perimeter of the endplate 250 for receiving insertable bone engagingmembers. In one embodiment, bone engaging members, comprise conicalspikes each having a cylindrical base portion configured to fit withinholes 286, for instance, by press-fit or by threaded engagement. Inalternate embodiments, differently shaped bone engaging members may beused, or in other embodiments no bone engaging members may be used.According to one preferred embodiment, endplate 250 has chamfered edges288 around the perimeter to facilitate insertion and/or accommodate theshape of the vertebral bodies which they engage. The superior or boneengaging surfaces 290 of endplate 250 may also include numerous types oftexturing to provide better initial stability and/or grasping contactbetween the end plate and the respective vertebrae. In a preferredembodiment, the texturing is a plurality of teeth 292. In preferredembodiments where the implant is manufactured from PEEK or other plasticmaterials, the endplate 250 may also include radio-opaque material, suchas tantalum markers 294, which aid in providing location markers inradiographic images.

In an exemplary use, during the implant installation and expansion tothe desired position, the endplate 250 can move in poly-axial fashionwith respect to the implant to accommodate the anatomy of the adjacentvertebral body as well as accommodate the natural curvature of thespine, such as kyphosis and lordosis. More specifically, the arcuateextension portion 252 is free to move in the interior portion 253 of thereceiving portion 254. The fingers 262 are generally compliant and canflex to accommodate the movement of the arcuate extension portion 252.Once the desired positioning of the endplate 250 is achieved, theendplate 250 can be locked in place. The endplate 250 is locked in placeby actuating the locking element 284. As the element 284 engages thethreading in opening 280, 282 the ends 277, 279 of the locking ring 256are brought closer together contracting the ring 254 and reducing thesize of the interior portion 255. As the ring 254 contracts, the fingers262 of the receiving member 254, abutting against the inner wall 268,are flexed radially inwardly pushing against the extension portion 252.As a result, the endplate 250 is locked in place.

While the invention herein disclosed has been described by means ofspecific embodiments and applications thereof, numerous modificationsand variations can be made thereto by those skilled in the art withoutdeparting from the scope of the invention as set forth in the claims.

What is claimed is:
 1. An expandable prosthetic implant for engagementbetween vertebrae, comprising: an inner member having a hollow interiorportion and a threaded external portion and including a first endportion configured to engage a first vertebral body; an outer memberhaving a hollow interior portion configured to coaxially receive theinner member therein and including a second end portion configured toengage a second vertebral body, wherein the inner and outer members aremoveable relative to each other along a longitudinal axis; a gear memberpositioned coaxial to the inner member and outer member and axiallyfixed to the outer member and freely rotatable with respect to the outermember; a locking member received in the outer member, the lockingmember having an engagement member; wherein the gear member threadedlyengages the threaded portion of the inner member, and a plurality ofcutouts capable of being engaged by the engagement member, wherein thefirst and second end portions are configured to respectively engagefirst and second vertebrae, wherein the implant is configured to engagethe vertebrae such that first and second end portions are oriented in apredetermined alignment with respect to the first and second vertebralbodies, wherein the gear member includes gear teeth extending around theperimeter of the gear member, the gear teeth extending from a proximalend of the gear member to a distal end of the gear member, wherein in afirst position, the engagement member of the locking member is receivedin the cutout of the gear member preventing the gear member fromrotating and in a second position, the engagement member of the lockingmember is not received in the cutout of the gear member allowing thegear member to rotate.
 2. The implant of claim 1, wherein the first endportion of the inner member or the second end portion of the outermember comprises an annular shaped endplate.
 3. The implant of claim 1,wherein the inner member includes a flattened portion and the outermember includes a flattened portion, wherein each of the flattenedportions cooperate to prevent rotational movement of the inner memberwith respect to the outer member.
 4. The implant of claim 1, wherein theinner member includes a base portion having at least one lobe and theouter member includes at least one depression, the lobes and depressioncooperate to prevent rotational movement of the inner member withrespect to the outer member.
 5. The implant of claim 1, wherein theouter member has an outer surface with at least one slot and an openingconfigured and dimensioned to receive a portion of an implantation tool.6. The implant of claim 1, wherein the outer member has a first endportion with a lip formed around the exterior of the first end portionconfigured to cooperatively fit with a portion of the gear member. 7.The implant of claim 6, wherein a plurality of relief spaces is radiallyspaced around the lip.
 8. The implant of claim 1, wherein the gearmember includes a helical thread along at least part of an inner wall.9. The implant of claim 1, wherein a first endplate is positioned on thefirst end portion of the inner member and a second endplate ispositioned on the second end portion of the outer member.
 10. Theimplant of claim 9, wherein an outermost diameter of the gear member isas large as an outer diameter of the first and second endplates.
 11. Anexpandable prosthetic implant for engagement between vertebrae,comprising: an inner member having a hollow interior portion and athreaded external portion and including a first end portion configuredto engage a first vertebral body; an outer member having an opening anda hollow interior portion configured to coaxially receive the innermember therein and including a second end portion configured to engage asecond vertebral body, wherein the inner and outer members are moveablerelative to each other along a longitudinal axis; a gear memberpositioned coaxial to the inner member and outer member and axiallyfixed to the outer member and freely rotatable with respect to the outermember; a locking member received in the outer member, the lockingmember having an engagement member engageable with a plurality ofcutouts in the gear member, wherein the gear member threadedly engagesthe threaded portion of the inner member, and wherein in a firstposition, the engagement member of the locking member is received in oneof the plurality of cutouts preventing the gear member from rotating andin a second position, the engagement member of the locking member is notreceived in one of the plurality of cutouts allowing the gear member torotate.
 12. The implant of claim 11, wherein the first end portion ofthe inner member or the second end portion of the outer member comprisesan annular shaped endplate.
 13. The implant of claim 11, wherein theinner member includes a flattened portion and the outer member includesa flattened portion, wherein each of the flattened portions cooperate toprevent rotational movement of the inner member with respect to theouter member.
 14. The implant of claim 11, wherein the inner memberincludes a base portion having at least one lobe and the outer memberincludes at least one depression, the lobes and depression cooperate toprevent rotational movement of the inner member with respect to theouter member.
 15. The implant of claim 11, wherein the outer member hasan outer surface with at least one slot and an opening configured anddimensioned to receive a portion of an implantation tool.
 16. Theimplant of claim 11, wherein the outer member has a first end portionwith a lip formed around the exterior of the first end portionconfigured to cooperatively fit with a portion of the gear member. 17.The implant of claim 16, wherein a plurality of relief spaces isradially spaced around the lip.
 18. The implant of claim 11, wherein thegear member includes a helical thread along at least part of an innerwall.
 19. The implant of claim 11, wherein a first endplate ispositioned on the first end portion of the inner member and a secondendplate is positioned on the second end portion of the outer member.20. The implant of claim 19, wherein an outermost diameter of the gearmember is as large as an outer diameter of the first and secondendplates.